In recent years, various devices including memory circuits, logic circuits, and image sensors (e.g., complimentary metal-oxide-semiconductor (CMOS) sensors) have become more and more highly integrated. In the processes of fabricating these devices, foreign matters, such as fine particles and dusts, may be attached to the devices. The foreign matters attached to the devices could be a cause of a short circuit between interconnects and a malfunction of the circuit. Therefore, in order to increase reliability of the devices, it is necessary to clean a wafer on which the devices are fabricated so as to remove the foreign matters from the wafer.
The foreign matters, such as fine particles and dusts, may also be attached to a backside surface of the wafer, i.e., a bare silicon surface. The foreign matters on the backside surface of the wafer may cause the wafer to be separated from a stage reference surface of an exposure apparatus and/or may cause the wafer surface to tilt with respect to the stage reference surface, resulting in a patterning shift or a focal length error. In order to prevent such problems, it is necessary to remove the foreign matters from the backside surface of the wafer as well.
There has recently been developed a patterning apparatus using nanoimprint technology, other than the optical exposure technology. In this nanoimprint technology, a mold, which has predefined interconnect patterns, is pressed against a resin material formed on a wafer to transfer the interconnect patterns to the resin material. In such nanoimprint technology, it is required to remove the foreign matters existing on the surface of the wafer in order to avoid transfer of unwanted spots between the mold and the wafer and also between wafers.
Heretofore, it has been customary to scrub a wafer with a pen-shaped brush or a sponge roll while rotating the wafer about its own axis. However, these conventional cleaning techniques have a low foreign matter removal ratio and particularly have found it difficult to remove foreign matters having a size of 100 nm or larger.